Acoustic wave resonators such as surface acoustic wave (SAW) resonators and piezoelectric thin film resonators are used as filters or duplexers having excellent high-frequency characteristics. In recent years, the reduction in size of mobile communications terminals requires a circuit that processes RF (Radio Frequency) signals, and an assembly of electronic components that constitutes the high-frequency circuit to be downsized. The circuit and the assembly of electronic components may be downsized by using a composite electronic component (sometimes referred to as a module) having functional elements such as filters or duplexers integrated and mounted on a single circuit substrate. Japanese Patent Application Publication No. 2002-198774 discloses a technique that mounts an element composed of a SAW filter, and a passive element such as a capacitor on a single substrate.
However, the conventional technique may form an open space between electronic components mounted on a circuit substrate depending on a configuration of an electronic circuit composed of the electronic components and the type of each electronic component. Such an open space may reduce a mechanical strength, especially a bending strength of the composite electronic component, and make the composite electronic component difficult to handle in a test equipment or to handle when mounted on an electronic device.